Reset issue is now confirmed. seems that the I2C lines leaks enough supply voltage to the oled controller chip.
I have simple RC circuit on reset pin connected to the 1.8V regulated supply, but seems that it does not go low enough to fully reset the chip. When writing bad register values, those are not going back to reset values unless the toh is completely removed from phone for about 30 sec.
Might need to add there active reset driver or something... have to check for a good and lowcost solution. maybe MCP120 or similar.
(note to self: RT9818C-29GV)